From a2f7e37d8adf2047e1f3b0ea1227ac9d51514783 Mon Sep 17 00:00:00 2001
From: Matthew Wozniak <me@woz.blue>
Date: Fri, 1 Nov 2024 13:47:31 -0400
Subject: play demo using the demoplayer object

---
 api.c | 44 +++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 39 insertions(+), 5 deletions(-)

(limited to 'api.c')

diff --git a/api.c b/api.c
index af7bb5e..8001f8f 100644
--- a/api.c
+++ b/api.c
@@ -6,16 +6,50 @@
 #undef NO_EXTERNS
 #include "os.h"
 #include "log.h"
+#include "sst/x86.h"
 
-struct engserver *engserver;
+struct engserver *engserver = NULL;
+struct engclient *engclient = NULL;
+struct demoplayer *demoplayer = NULL;
+void (*cbuf_addtext)(char *) = NULL;
 
-void api_init() {
-	void *engine_dll = os_dlopen("engine");
+bool api_init(void) {
+	void *engine_dll = os_dlhandle("engine");
 	createinterface_func engine_factory =
 		(createinterface_func)os_dlsym(engine_dll, "CreateInterface");
-	if (!engine_factory) die("couldn't get engine factory");
+	if (!engine_factory) bail("couldn't get engine factory");
 	engserver = engine_factory(INTERFACEVERSION_VENGINESERVER, NULL);
-	if (!engserver) die("couldn't get IVEngineServer from engine");
+	if (!engserver) bail("couldn't get IVEngineServer from engine");
+	engclient = engine_factory(VENGINE_CLIENT_INTERFACE_VERSION, NULL);
+	if (!engclient) bail("couldn't get IVEngineClient from engine");
+
+	// find cbuf_addtext
+	const u8 *instr = (const u8 *)engserver->vt->server_command;
+	// ServerCommand() calls a few small functions before Cbuf_AddText but they
+	// get inlined. look for 'push esi' and then a call.
+	for (const u8 *p = instr; p - instr < 64;) {
+		if (*p == X86_PUSHESI && *++p == X86_CALL) {
+			// jump is relative to after the instruction
+			cbuf_addtext = (void (*)(char *))(p + 5 + *(i32 *)(p + 1));
+		}
+		int l = x86_len(p);
+		if (l == -1)
+			bail("invalid instruction looking for cbuf_addtext");
+		p += l;
+	}
+	if (!cbuf_addtext) bail("couldn't find cbuf_addtext");
+
+	// find demoplayer
+	instr = (const u8 *)engclient->vt->is_playing_demo;
+	debug("is_playing_demo = %p", (void *)instr); 
+	// CEngineClient::IsPlayingDemo is a wrapper around a demoplayer call
+	// The first thing it does should be load demoplayer into ECX
+	if (instr[0] != X86_MOVRMW || instr[1] != X86_MODRM(0, 1, 5))
+		bail("couldn't get demoplayer");
+	demoplayer = **(struct demoplayer ***)(instr + 2);
+	debug("demoplayer = %p", (void *)demoplayer);
+	
+	return true;
 }
 
 // vi: sw=4 ts=4 noet tw=80 cc=80
-- 
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